Epistasis: Gene Masking

Correct Answer: Epistasis

Epistasis is a type of non-allelic (intergenic) interaction where one gene masks the expression of another non-allelic gene. It is a form of non-additive gene action (NAGA).

Key Distinction from Dominance

• Dominance: Masking between alleles at the same locus (intragenic/intra-allelic interaction)
• Epistasis: Masking between genes at different loci (intergenic/inter-allelic interaction)

F2 Phenotypic Ratios for Epistasis Types (from Table 10)

• Dominant epistasis → 12:3:1
• Recessive epistasis / Supplementary gene action → 9:3:4
• Complementary gene action → 9:7
• Duplicate gene action → 15:1
• Inhibitory gene action → 13:3

Why Other Options Are Wrong

• Dominance: Intra-allelic interaction, not inter-allelic.
• Pleiotropy: One gene controlling multiple traits (e.g., halothane gene in pigs, sickle cell anemia gene in humans, double muscling gene in cattle).
• Linkage: Two genes on same chromosome — exception to Mendel's law of independent assortment.